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Field  Museum  of  Natural  History 

Museum  Technique  Series 

No.  2 


NEW  USES  OF  CELLULOID  AND  SIMILAR 
MATERIAL  IN  TAXIDERMY 


BY 


Leon  L.  Walters 
Taxidermist,  Division  of  Reptiles 


Wilfred  H.  Osgood 
Curator,  Department  of  Zoology 

EDITOR 


Chicago,  U.  S.  A. 

June.    TQ25 


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Field  Museum  of  Natural  History 


Museum  Technique  Series 

No.  1 


NEW  USES  OF  CELLULOID  AND  SIMILAR 
MATERIAL  IN  TAXIDERMY 


BY 

Leon  L.  Walters 
Taxidermist,  Division  of  Reptiles 


Wilfred  H.  Osgood 
Curator,  Department  of  Zoology 

EDITOR 


Chicago,  U.  S.  A. 

June,  1925 


Tit,  Z- 


NEW  USES  OF  CELLULOID  AND  SIMILAR 
MATERIAL  IN  TAXIDERMY 


BY   LEON   L.  WALTERS 


The  present  paper  deals  especially  with  the  correlation  of  form 
and  color  in  making  replicas  of  natural  objects.  When  this  was 
first  put  into  practice,  in  preparing  small  reptiles,  celluloid  was  used  as 
a  medium  in  conjunction  with  pigment.  The  process  has  become  rather 
generally  known  as  "the  celluloid  process,"  although,  strictly  speaking, 
celluloid  is  only  one  of  various  materials  that  have  been  employed.  In 
explaining  this  process,  it  is  hoped  not  only  to  give  practical  suggestions 
for  actual  work,  but  to  bring  about  a  clearer  understanding  of  the  re- 
lation of  form  and  color  as  they  exist  in  the  natural  object. 

Taxidermy  has  realism  as  its  ideal  and  so  every  factor  that  con- 
tributes to  what  we  see  in  a  living  creature  should  be  isolated  and 
studied.  This  brings  up  the  question  of  just  what  constitutes  all  we 
see  or  regard  as  "life"  or  the  appearance  of  life  in  the  living  model. 
Among  animals  many  subtle  phenomena  exist.  How  much  or  how  little 
any  of  them  may  actually  contribute  to  our  impression  is  speculative. 
If  there  be  anything  not  expressed  through  form  or  color,  it  cannot 
be  translated  into  glass,  marble,  celluloid,  metals  or  other  materials 
available  to  the  taxidermist  or  sculptor.  Motion,  which  is  almost  insep- 
arable from  the  majority  of  subjects,  has  the  greatest  influence  in 
forming  our  impressions ;  but  we  cannot  have  motion.  Allowing  for 
a  suspense  of  motion,  however,  it  is  not  established  that  the  entire  ap- 
pearance of  life  does  not  lie  within  the  limits  of  the  various  intricacies 
of  form  and  color.  It  may  be  conceded  that  attempts  to  secure  the  ap- 
pearance of  life  fall  short  of  absolute  realism,  but  before  forming  a 
theory  to  explain  the  failure,  it  should  be  made  entirely  certain  that 
technical  shortcomings  are  not  responsible  for  what  may  be  lacking. 
We  accept  many  parts  of  a  replica  as  being  perfect.  The  replica,  itself, 
may  be  but  a  part,  such  as  an  artifical  human  eye.  Each  feature  will 
be  compared  with  the  real  eye.  If  we  can  appreciate  or  suspect  a  differ- 
O      ence,  can  we  not  finally  resolve  and  attribute  this  difiference  to  some 


K? 


1 


4       Field  Museum  of  Natural  History — Technique,  No.  2, 

specific  fault  in  color,  translucence,  form,  proportion  or  marking?  The 
difference  may  finally  be  found  to  be  due  only  to  the  lack  of  contraction 
and  expansion  in  the  pupil. 

Form  refers  to  the  general  bulk  of  the  figure,  its  anatomical  struc- 
ture, posture  or  attitude,  and  also  deals  with  the  most  minute  details 
of  the  surface.  In  color,  besides  the  correct  tint,  we  are  concerned 
with  duplicating  the  particular  degree  of  translucence  that  is  found  in 
the  various  visible  parts  of  the  specimen.  Pigments,  as  prepared  for 
normal  Use,  are  very  opaque  materials.  Although  mixed  with  oils  or 
varnishes,  their  opacity  is  not  appreciably  reduced.  Natural  objects  on 
the  other  hand  are  relatively  translucent  and  in  them  the  coloring  agents 
are  scattered  through  a  layer  of  considerable  thickness,  the  colored  parts 
having  the  appearance  of  being  lightly  pigmented.  If  a  thin  shaving  is 
cut  from  the  surface  of  a  natural  object,  the  shaving  will  appear  much 
less  colored  than  the  normal  area  surrounding  it.  Quite  a  thick  layer 
may  be  necessary  to  secure  the  full  color  effect.  It  is  found  that  by 
taking  artificial  pigments,  correct  as  to  tint,  and  mixing  them  with  the 
proper  quantity  of  translucent  material,  a  result  can  be  obtained  that, 
so  far  as  the  eye  is  concerned,  will  equal  the  object  to  be  duplicated. 

We  will  assume  that  the  various  considerations  regarding  form 
have  been  dealt  with  and  that  a  mold  of  the  object  has  been  made.  If 
we  make  a  cast  from  this  mold,  its  form  will  be  exactly  that  of  the  ob- 
ject from  which  the  mold  was  made.  While  the  form  is  correct,  the  cast 
has  only  the  monochrome  color  of  the  material  used  in  its  making.  It 
is  then  necessary  to  color  the  cast,  but  any  coating  of  pigment,  however 
slight,  rises  above  what  may  be  called  the  true  surface  and  the  form 
is  no  longer  correct.  This  change  of  form  may  not  be  great  or  may 
not  be  perceptible  when  translucence  is  sacrificed  and  the  most  opaque 
pigments  are  used  for  the  coloring.  However,  it  has  been  found  that 
in  the  average  instance,  a  thick  coating  of  coloring  material  is  required 
for  the  correct  color  qualities.  This  thick  coating  very  decidedly  alters 
the  fine  surface  details  of  the  cast.  While  a  model  of  translucent  or 
partly  colored  materials,  such  as  celluloid  or  wax,  could  be  cast  in 
the  normal  way,  there  would  yet  remain  the  matter  of  applying  the 
colors  that  are  at  variance  with  the  general  color  selected.  In  this  we 
have  the  problem  jlist  presented.  To  color  the  finished  cast  through 
the  use  of  dyes  would  not  necessarily  alter  the  surface  form.  How- 
ever, it  will  be  shown  that  different  colored  bodies  of  varying  degrees 
of  pigmentation  exist  in  definite  locations  beneath  the  surface.  The 
surface  layer  may  be  translucent  and  practically  uncolored,  the  main 
coloration  existing  directly  beneath  this  surface  layer.    Very  often  the 


IHE  UBRAiit  BF  THE 
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Celluloid  in  Taxidermy — Walters.  5 

different  layers  are  of  strongly  contrasting  colors  and  the  color  effect 
of  the  whole  is  due  to  this  particular  arrangement.  Dyes  would  neces- 
sarily color  these  surface  layers  as  well  as  the  deeper  portions. 

The  obvious  solution  of  the  color  problem  is  to  apply  colors  to 
the  mold  and  not  to  the  finished  cast.  Each  color  is  applied  or  painted 
in  its  proper  location  on  the  interior  surface  of  the  mold.  In  the  final 
result  the  surface  details  remain  unimpaired,  all  the  colors  appearing 
within  the  true  surface.  But  slight  reflection  is  needed  to  see  that  this 
condition  prevails  in  the  natural  object.  This  briefly  presents  the 
fundamental  principle  of  the  process.  After  the  application  of  the 
materials  necessary  to  secure  the  full  color  appearance,  layers  of  other 
materials,  such  as  cloth  and  wire-cloth  are  added  for  further  strength 
and  support.  The  replica,  entirely  complete  as  to  coloration,  is  then 
removed  from  the  mold. 

Problems  of  Form. 

Field  and  laboratory  studies  of  living  animals. — If  the  exhibit  is 
to  have  its  greatest  value,  it  is  essential  that  studies  be  made  of  the 
animal  in  its  natural  home.  The  selection  of  an  interesting  phase  of 
its  life  from  a  biological  or  from  an  artistic  standpoint  is  made  from 
such  studies.  The  animals'  habits  may  be  well  known  and  the  general 
character  of  the  exhibit  may  be  determined  upon  beforehand,  but  even 
then,  it  is  necessary  to  supply  by  direct  observation  and  attention  the 
innumerable  details  that  are  necessary  to  a  truthful  and  convincing 
reproduction.  Such  studies  have  the  same  relation  and  importance  to 
the  museum  preparator  that  personal  sittings  and  studies  have  to  the 
portrait  painter  or  sculptor.  With  reptiles  and  amphibians  field  studies 
can  be  supplemented  very  favorably  by  further  studies  of  caged  speci- 
mens in  the  laboratory,  but  allowance  must  be  made  for  the  abnormal 
conditions.  The  value  of  such  studies  is  mainly  in  the  anatomical 
structure  and  details  for  Use  in  coloring.  In  a  general  way,  frogs  and 
toads  can  be  expected  to  act  in  a  fairly  normal  way  in  surroundings 
that  can  be  made  nearly  natural  for  them.  The  behavior  of  lizards 
may  be  expected  to  be  farthest  from  normal. 

In  the  course  of  studies  made  by  Mr.  Karl  P.  Schmidt  and  myself, 
in  Central  America,  we  observed  that  a  captive  crocodile  did  not  walk 
but  progressed  by  short  rushes.  However,  Under  natural  undisturbed 
conditions,  crocodiles  would  swim  to  the  edge  of  the  water,  stand 
high  upon  their  legs  and  walk  out  on  the  bank.  This  dinosaur-like 
position  assumed  in  walking  was  surprising  and  interesting  and  was 
chosen  for  one  of  the  specimens  for  a  group.    These  crocodiles  would 


6       Field  Museum  of  Natural  History — Technique,  No.  2. 

lie  on  the  bank  for  hours  at  a  time,  holding  the  mouth  open.  This 
peculiar  habit  is  interesting,  displays  the  interior  of  the  mouth  and 
shows  the  peculiar  structure  of  the  throat  valve.  The  crocodiles  would 
also  lie  motionless  in  the  water  with  only  the  nostrils  and  eyes  ex- 
posed. This  shows  an  interesting  adaptation  to  an  aquatic  existence. 
These  were  the  primary  reasons  for  selecting  the  positions  chosen  for 
the  reproductions.  In  the  case  of  these  crocodiles,  plaster  was  trans- 
ported and  molds  of  the  reptiles  were  made  on  the  bank  of  the  lake 
where  they  were  collected.  Skins  were  preserved  for  pattern,  and  color 
notes  were  taken  for  later  use  in  making  the  reproduction.  Large 
specimens  such  as  these  present  difficulties  connected  with  the  large 
amount  of  plaster  required  and  the  extra  care  necessary  in  packing  the 
molds  for  shipment.  The  alternative  is  to  remove  the  skin  and  pre- 
serve it  together  with  the  skeleton  and  data  for  its  rebuilding  in  the 
laboratory.    The  plaster  mold  is  then  made  from  a  reconstructed  form. 

The  Use  of  live  specimens  presents  a  number  of  advantages  in  this 
work  where  color  is  so  important,  and,  fortunately,  live  specimens  are 
very  readily  available  among  reptiles  and  amphibians.  Ordinarily 
they  are  captured  alive  when  collected.  They  can  be  kept  captive  in 
a  sack  or  box  and  can  be  shipped  without  provision  for  feeding.  Am- 
phibians can  be  shipped  in  cans  containing  dampened  moss,  the  lids 
punctured  from  the  inside  with  holes  for  ventilation.  All  are  easily 
kept  in  the  laboratory,  a  feeding  of  once  or  twice  a  week,  ordinarily, 
being  sufficient  to  keep  them  in  good  condition.  Occasional  specimens 
do  not  do  well  and  soon  become  emaciated.  The  plaster  molding  must 
be  done  before  this  occurs,  for  if  no  other  specimen  is  available,  it 
will  be  necessary  before  molding  to  remove  the  skin  and  adjust  it 
on  a  carefully  prepared  clay  model,  a  contingency  to  be  avoided  if 
possible.  In  most  instances,  a  mold  of  a  reptile  or  amphibian  can  be 
satisfactorily  made  directly  from  a  freshly  killed  specimen. 

Selection  of  specimens. — It  is  desirable  that  the  specimen  be  in 
normal  physical  condition  and  present  the  average  size  of  the  species. 
It  should  be  neither  a  record  specimen  as  to  size  nor  be  much  under 
the  average.  Care  should  be  taken  to  retain  the  relative  sizes  of  the 
species  represented.  An  undersized  specimen  may  be  used  as  possibly 
being  the  best  available  at  the  time.  Also,  an  oversized  specimen 
of  another,  although  smaller,  species  may  be  used.  It  seems  a  small 
matter  at  the  time  but,  later,  these  specimens  will  be  exhibited  side 
by  side  in  the  same  case,  and,  with  reptiles  as  with  fish,  relative  size 
is  one  of  the  points  strongly  impressed  on  the  observer.     The  more 


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careful  and  detailed  the  technical  work  in  the  reproduction  and  the 
accessories,  the  more  confidence  the  observer  will  have  in  other 
features  of  the  work.  The  same  applies  to  coloration.  Often  it  may 
be  necessary  to  consider  exhibition  of  more  than  one  specimen  in  order 
to  cover  the  color  variations,  especially  if  distinct  color  phases  exist. 
A  study  of  the  species  in  regard  to  relationship  or  taxonomy  is  neces- 
sary to  determine  and  fully  represent  the  characters  of  greatest  im- 
portance. The  number  of  exhibits  that  can  be  prepared  is  limited. 
Therefore,  considerable  care  should  be  exercised  in  study  of  the  species 
and  in  selecting  the  specimen  that  is  to  be  perpetuated. 

Composition  and  pose. — After  studies  have  been  made  of  the 
subject  in  the  field,  some  interesting  trait  or  habit  desirable  to  represent 
will  nearly  always  be  discovered.  This  is  the  direct  result  of  study 
of  the  animal  in  its  natural  habitat  and  involves  judgment  in  selecting 
what  is  best  to  represent,  due  regard  being  given  to  technical  problems 
of  reproducing  and  final  installation  in  the  museum.  The  personal 
equation  barely  enters  in  the  positioning  of  the  specimen.  This  was 
the  case  in  regard  to  the  crocodiles  referred  to,  although  here,  personal 
ideas  are  allowed  some  play  in  selecting  and  arranging  the  ground 
work  and  in  arranging  the  specimens  upon  it. 

In  deaHng  with  snakes,  however,  we  have  an  additional  problem. 
Few  snakes  have  distinctive  habits  that  would  lead  to  an  immediate 
choice  of  position.  A  cobra  might  logically  be  posed  in  its  charac- 
teristic attitude  with  the  forward  part  of  the  body  reared  off  the  ground 
and  the  hood  spread.  The  rattlesnake  has  a  characteristic  position 
when  it  takes  the  defensive,  the  body  being  tightly  coiled  and  the  neck 
and  head  taking  the  form  of  the  letter  S.  It  would  be  very  well  to 
illustrate  two  or  three  of  the  dozen  or  so  species  that  exist,  in  this 
position.  Many  snakes  that  live  on  the  ground  have  no  peculiar  or 
distinctive  habits  that  would  lead  to  a  choice  of  a  position.  It  is  with 
such  as  these  that  the  personal  element  enters  and  the  specimen  is 
arranged  according  to  the  ideas  of  the  individual  in  regard  to  compo- 
sition or  design.  The  snake  lends  itself  readily  to  an  almost  unlimited 
variety  of  positions  that  are  anatomically  correct.  Diverse  angles  and 
curves,  when  carried  out  in  the  arrangement  of  a  snake,  are  usually 
accepted  as  giving  the  most  pleasing  design,  and  if  the  casual  opinion 
of  a  number  of  persons  is  asked,  nearly  all  will  agree  that  certain 
arrangements  are  decidedly  more  pleasing  than  others.  The  same  in- 
fluences that  are  common  in  regard  to  design  in  art  apply  here.  Used 
judiciously  and  closely  limited,  design,  while  in  itself  having  no  relation 
to  the  problem  of  making  a  truthful  natural  history  reproduction,  may 


8       Field  Museum  of  Natural  History — Technique,  No.  2. 

become  an  asset,  but  when  persisted  in  without  close  restraint  through- 
out an  entire  series,  the  effect  is  monotonous  and  displeasing.  An 
injudicious  display  of  this  tendency  is  unfortunately  in  evidence  in 
nearly  all  work  on  snakes.  In  any  event,  the  specimen  should  never 
have  the  appearance  of  being  designed,  and  it  is  better  not  to  use 
theories  and  ideas  in  regard  to  design  that,  in  this  work,  would  produce 
a  recognizable  similarity  and  duplication  when  a  number  of  specimens 
finally  occupy  a  single  case. 

Preparation  of  the  specimen  for  molding. — The  preparation  of  the 
specimen  for  molding  and  the  working  of  the  molding  material  are 
of  great  importance.  If  the  model  cannot  be  brought  to  a  state  en- 
tirely satisfactory  as  to  form,  the  reproduction  will  necessarily  preserve 
the  same  objectionable  features.  If  detailed  surface  form  is  lacking 
or  is  lost  through  poor  molding,  then  this  process  will  be  of  little 
utility.  Before  molding,  the  specimen  should  be  fully  restored  to  life- 
like condition  in  so  far  as  form  is  concerned.  As  in  all  taxidermy,  a 
thorough  study  and  familiarity  with  anatomy  in  relation  to  modelling  is 
necessary.  Even  when  a  mold  is  to  be  taken  immediately  after  the 
death  of  a  reptile,  it  is  necessary  to  study  during  life  the  positions  of 
all  the  parts  that  would  be  influenced  by  death,  so  that  before  molding 
they  can  be  restored  to  their  life-like  positions.  Failure  to  detect  the 
small  changes  that  take  place  after  death  and  to  restore  them  is  one 
of  the  reasons  why  casts  have  been,  in  general,  unfavorably  considered. 
Restoration  of  the  eyes,  for  example,  to  their  life-like  position  is  nearly 
always  slighted.  Among  amphibians  and  reptiles,  with  the  exception 
of  snakes,  the  eyes  are  retracted  on  the  death  of  the  specimen.  The 
eyeball  mtist  be  brought  to  its  natural  position  before  molding.  It 
may  be  necessary  to  cut  certain  of  the  eyelid  muscles,  or  to  entirely 
remove  the  natural  eyeball  and  replace  with  an  artificial  eye.  Proper 
support  of  the  abdomen,  throat  and  other  parts  must  be  provided.  If 
this  cannot  be  accomplished  with  the  freshly  killed  specimen,  the  remedy 
is  to  make  the  necessary  studies,  remove  and  preserve  the  skin  and, 
later,  in  the  laboratory,  adjust  this  skin  on  a  reconstructed  clay  figure. 
When  this  is  contemplated,  the  skeleton  should  be  saved  to  accompany 
the  skin  and  the  anatomical  studies  and  casts  that  are  made  in  the 
field.  The  fine  details  of  skin  texture  need  no  particular  attention  in 
fresh  specimens  except  with  frogs  and  toads  in  which  the  warts  often 
flatten  down  soon  after  death. 

All  possible  preparation  and  study  should  be  made  before  the 
specimen  is  killed  so  that  after  killing,  the  work  of  positioning,  re- 
storing and  molding  can  take  place  without  delay.     If  the  specimen  is 


Celluloid  in  Taxidermy — Walters.  9 

to  lie  on  a  branch  or  any  part  of  a  log,  the  selection  of  this  branch 
or  log  should  be  made  beforehand.  Details  of  the  position  can  be 
arranged  after  killing,  but  the  general  position  should  be  determined 
in  advance. 

Methods  of  killing. — In  killing  the  specimen,  the  requirements  are 
that  it  be  accomplished  as  readily  as  possible  and  that  after  death  the 
muscles  shall  be  relaxed.  Drowning  is  very  satisfactory  in  most  cases. 
During  the  winter  it  is  not  always  possible  to  do  this  unless  the  speci- 
men is  placed  in  warm  water,  as  at  that  season,  when  placed  in  cold 
water,  reptiles  and  amphibians  readily  pass  into  a  state  of  suspended 
animation  and  are  not  harmed.  A  saturate  solution,  about  i  to  100 
of  chloretone  (a  chloroform  deriviative)  and  water  is  useful,  especially 
for  amphibians.  Specimens  placed  in  this  liquid  are  quickly  killed 
and  the  muscles  are  left  relaxed.  Often  shortly  after  death,  warts 
and  protuberances  in  the  skin  of  frogs  and  toads  lose  their  plumpness 
and  full  size,  and  the  specimen  is  no  longer  useful  for  molding.  The 
molding  of  the  specimen  must  take  place  before  this  occurs. 

Use  of  skins  and  preserved  specimens. — Remarks,  so  far,  have  dealt 
mainly  with  the  Use  of  live  specimens  under  favorable  conditions. 
There  are  many  cases  where  live  specimens  cannot  be  obtained.  The 
only  available  material  may  be  in  the  form  of  an  old  mounted  specimen, 
a  dried  skin,  an  alcoholic,  a  fresh  salted  skin  or  a  skin  in  pickle.  When 
a  skin  has  been  allowed  to  dry,  the  surface  form  is  greatly  altered,  due 
to  the  wrinkling,  shriveling  and  flattening  that  takes  place.  With  the 
mounted  specimen  or  dried  skin,  the  skin  must  be  placed  in  a  bath, 
usually  of  salt  water  or  fresh  water  with  an  antiseptic  added  in  order 
to  soften  and  plump  it  to  a  condition  comparable  to  that  of  a  fresh 
skin.  When  this  is  accomplished,  as  in  the  majority  of  cases  it  can 
be,  a  clay  figure  is  constructed  and  the  skin  is  adjusted  and  modelled 
on  this  figure.  In  addition  to  softening  the  skin  sufiiciently  to  permit 
its  proper  adjustment,  the  finer  details  of  the  skin  surface,  of  tuber- 
osities, of  scales  and  wrinkles  must  be  plumped  to  their  original  full 
form  as  in  Hfe.  In  the  alcoholic  specimen,  the  details  of  the  skin  sur- 
face are  usually  well  preserved.  The  hardening,  due  to  action  of 
alcohol  and  other  preservatives,  such  as  formaldehyde,  must  be  suffi- 
ciently overcome  to  allow  for  the  manipulation  and  adjustment  of  the 
skin.  This  cannot  always  be  done,  but  long  soaking  in  salt  water  will 
greatly  improve  the  condition.  If  the  skin  is  a  freshly  salted  one,  or 
is  in  salt  brine  pickle,  it  is  only  necessary  to  wash  in  fresh  water 
sufficiently  to  remove  the  excess  salt.     With  dried  skins,  old  mounted 


lo     Field  Museum  of  Natural  History — Technique,  No.  2. 

specimens,  or  any  skins  in  doubtful  condition  it  is  generally  possible 
to  remove  a  part  for  preliminary  experimentation.  While  such  skins 
can  be  brought  to  a  condition  in  regard  to  the  surface  details  of  form 
that  would  be  a  great  improvement  over  their  previously  shrunken  and 
shriveled  state,  it  is  not  always  possible  to  bring  them  to  the  condition 
desired.  The  importance  of  these  details  cannot  be  minimized.  Any 
treatment  of  the  skin  that  has  an  astringent  action,  or  even  the  slightest 
drying,  results  in  changes  of  form  that  are  universally  characteristic. 
The  eye  generally  recognizes  even  the  smallest  changes  that  take  place, 
although  the  mind  may  not  be  able  to  readily  analyze  and  point  out 
these  changes. 

With  extremely  rare  species,  it  would  be  possible  to  restore  a 
specimen,  approximately,  even  by  resorting  to  modeling  the  skin  sur- 
face, but  cases  warranting  such  expenditure  of  time,  coupled  with  the 
inevitable  inaccuracies,  will  be  very  few  or  none.  Usually  such  speci- 
mens lack  reliable  color  notes  or  other  data  for  proper  anatomical 
construction  of  the  figure  and  correct  posing  in  a  natural  surrounding. 
A  scientific  institution  has  no  need  or  desire  to  wander  too  far  from 
the  paths  of  actuality  in  its  exhibits  any  more  than  in  any  other  branch 
of  its  work.  A  fabrication  in  form  and  color  can  be  no  less  a  mis- 
representation than  if  it  were  in  written  words.  The  worker  should 
know  the  requirements  of  his  work  to  the  extent  that  he  can  determine 
what  he  can  do  and  what  he  cannot  do  with  the  material  available. 
He  should  recognize  the  difficulties  with  each  particular  piece  of  work 
and  determine,  beforehand,  whether  or  not  he  is  in  a  position  to  over- 
come these  difficulties  in  a  reasonable  manner.  Lacking  usable  data 
regarding  the  life  or  habits  of  the  species,  he  supplies  it  if  he  can. 
He  looks  up  color  descriptions  and  checks  up  color  notes  with  markings 
that  may  remain  on  alcoholics  to  determine  whether  or  not  he  can  use 
them  with  assurance  of  a  reasonable  degree  of  accuracy.  A  skeleton 
and  photographs  may  supply  information  as  to  anatomical  construction, 
while  the  skin  itself  or  a  small  sample  of  it  can  be  experimented  with 
in  order  to  discover  whether  or  not  it  can  be  plumped  to  a  condition 
in  which  the  surface  detail  will  approximately  equal  that  of  life.  Even 
with  everything  else  satisfactory,  there  may  be  some  outstanding  prob- 
lem in  connection  with  the  color  which  the  experience  and  experi- 
mentation of  the  worker  at  the  time  may  not  be  sufficient  to  solve. 
It  is  wise  then  to  drop  that  particular  job  and  turn  to  something  else 
that  can  be  done  properly.  At  a  later  time  a  way  may  be  discovered 
to  overcome  the  previous  technical  difficulty  or  supply  the  missing 
information.     Then  it  is  time  to  do  the  work.     At  the  best,  there  are 


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.li!L  24  1926 

UNIVERSITY  OF  ilUUm 


Celluloid  in  Taxidermy — Walters.  ii 

many  technical  complications  and  difficulties  in  the  work  of  making  a 
reproduction  of  this  kind,  and  in  spite  of  the  greatest  care,  a  large 
percentage  of  errors  will  creep  in. 

While  this  process  may  appear  to  be  primarily  a  process  of  coloring, 
it  must  be  remembered  that  the  great  object  of  the  difficult  and  tedious 
application  of  the  colors  to  the  interior  of  the  mold  is  preservation 
of  the  details  of  correct  form.  Anything  unsatisfactory  in  the  form 
will  be  perpetuated  in  the  reproduction.  The  particular  defect  will 
stand  out  above  all  merits,  and  the  specimen  will  be  remembered  by 
its  faults  rather  than  its  virtues.  Features  that  are  correct  are  passed 
by  without  particular  thought  except  to  note  that  they  are  as  was 
intended. 

Molding. — The  molding  is  a  vital  step  between  the  original  model 
and  its  final  reproduction.  No  matter  how  satisfactory  the  model  may 
be,  defective  molding  will  ruin  the  result.  In  any  case,  the  final  form 
will  be  no  better  than  that  obtained  in  the  mold.  The  making  of 
plaster  molds  and  the  proper  handling  of  plaster  is  a  matter  of  ex- 
perience and  close  study.  It  may  be  years  before  a  careful  workman 
will  be  reasonably  satisfied  with  his  plaster  work.  Satisfaction  may 
often  mean  a  relinquishment  of  ideals  but  this  is  not  necessarily  so. 
It  would  be  futile  and  misleading  to  attempt  to  lay  down  rules  to  guide 
work  in  which  only  observation,  experience  and  long,  careful  study 
lead  to  results.  The  present  process  requires  the  mold  to  be  made  in 
such  manner  that  every  part  of  it  is  accessible  in  order  to  do  the 
coloring  that  follows.  Snakes,  turtles,  and  many  subjects  will  be  posed 
for  lying  positions  and  so  quite  an  area  of  the  under  surface  of  their 
bodies  is  hidden.  As  this  is  not  seen,  it  need  not  be  reproduced  and 
will  then  present  an  opening  through  which  much  of  the  coloring  can 
be  done.  The  head  and  neck  or  other  parts  must  be  made  in  sections, 
using  various  piece  mold  processes.  Often  it  is  possible  to  mold  the 
part  entire  with  strips  of  tin  or  lead  inserted  in  the  body  of  the  mold 
where  it  is  desired  to  have  the  line  of  separation.  The  strips  should 
not  quite  touch  the  specimen.  After  the  plaster  has  completely  set, 
separation  is  brought  about  by  breaking,  the  strips  of  tin  controlling 
the  line  of  fracture.  The  best  result  is  obtained  when  the  line  of 
fracture  disappears  on  joining  the  two  halves  thus  produced.  An 
objection  is  in  an  occasional  broken  fragment  which  must  be  saved 
and  replaced.  All  molding  must  be  done  without  disarranging  parts 
of  the  specimen  by  the  pressure  of  supports  or  dividing  strips. 

The  plaster  should  be  very  hard  when  set,  otherwise  a  film  may 
detach  and  remain  on  the  surface  of  the  specimen  and  points  may  be 


12     Field  Museum  of  Natural  History — Technique,  No.  2. 

broken  or  rubbed  off  when  the  specimen  is  removed  from  the  mold. 
Generally  speaking,  the  hardness  of  gypsum  plaster  is  in  proportion 
to  its  density,  and  so  it  is  desirable  to  use  the  minimum  amount  of 
water  consistent  with  the  requirements  of  handling.  Also,  a  thin 
section  of  plaster  will  be  harder  on  its  inner  surface  than  a  thicker 
section  of  the  same  plaster.  If  the  surface  of  the  specimen  is  smooth 
and  polished,  the  surface  of  the  mold  should  appear  glassy  and  pol- 
ished. The  mold  surface  should  be  free  from  bubbles.  One  of  the 
common  causes  of  surface  bubbles  is  the  adhesion  and  inclusion  of 
air,  mainly  in  cavities  between  scales  and  in  sharp  depressions.  These 
can  be  removed  by  applying  the  first  plaster  to  the  surface  and  into 
the  cavities  with  a  soft  brush  before  the  bulk  of  it  is  applied.  All 
but  the  smallest  molds  should  be  reenforced  with  a  plaster  and  fiber 
coating  as  a  precaution  against  breakage  in  handling. 

Many  amphibians  have  slimy  surface  secretions,  albuminous  in 
character,  that  prevent  the  proper  setting  of  plaster.  There  are  several 
ways  to  render  these  albuminous  substances  inactive  on  the  plaster. 
Treatment  with  a  coagulating  medium  previous  to  molding  is  apt  to 
cause  a  hardening  of  the  skin  and  bring  about  other  changes  detrimental 
to  form  and  the  easy  positioning  of  the  specimen.  Probably  the  best 
procedure  is  to  pose  the  specimen  as  quickly  as  possible  in  a  lifelike 
position  and  without  treatment  of  any  kind,  to  depend  on  a  coagulating 
medium  that  can  be  included  in  the  plaster  mixture.  Alum  seems  to 
serve  this  purpose  fairly  well.  Besides  acting  as  a  coagulant  of  the 
albumen,  it  combines  with  the  plaster,  causing  an  accelerated  and  more 
complete  recrystallization. 

The  colors,  bound  in  cellulose  nitrate  or  acetate,  can  be  painted  di- 
rectly upon  the  plaster  surface  of  the  mold,  although  it  is  occasionally 
advantageous  to  employ  a  method  of  separation,  the  principle  of  which 
was  employed  by  Carl  E.  Akeley  in  making  up  his  mammal  manikins 
and  which  is  in  general  use  today  in  manikin  work.  This  consists  in 
sizing  and  surfacing  the  mold  with  the  thinnest  possible  film  of  a 
material  that  is  imaffected  by  the  cellulose  acetate  or  nitrate  solvents 
used  in  making  the  model  and  is,  itself,  soluble  in  solvents  that  will 
have  no  effect  on  the  model.  In  ordinary  practice,  in  connection  with 
cellulose  acetate  or  nitrate  models,  when  the  model  is  completed  and 
ready  for  the  removal  of  the  mold,  the  mold  is  placed  in  water.  The 
water  softens  the  plaster  and  it  is  readily  broken  away  and  any  frag- 
ments of  plaster  still  adhering  to  the  reproduction  are  removed  with 
a  stiff  brush.  If  a  sizing  of  gelatine,  casein,  gum  arable  or  other  water 
soluble  material  has  been  used,  this  sizing  is  dissolved   on  the   final 


Celluloid  in  Taxidermy — Walters.  13 

soaking  of  the  mold  in  water,  thus  cleanly  releasing  the  model  from 
the  mold. 

Coloring  Problems. 

General  problems. — In  making  replicas  of  natural  objects,  such  as 
are  now  being  considered,  coloration  requires  altogether  different  pro- 
cedure from  that  for  which  pigments  are  designed  and  normally  used. 
Ordinary  painting  is  coloring  a  surface  with  a  coating  of  pigment 
mixed  with  a  drying  oil  or  varnish,  either  for  protection  or  for  the 
purpose  of  decoration.  Other  things  being  equal,  the  pigments  most 
desired  for  use  in  painting  are  those  that  when  finely  divided  have 
the  greatest  covering  power.  It  is  among  these  commercial  pigments 
that  we  find  our  coloring  agents,  but  their  use  in  the  usual  manner  is 
impossible. 

Throughout  nature,  we  have  relatively  few  objects  that  present 
the  same  appearance  to  the  eye.  Form  is  often  the  primary  means  of 
identification.  However,  with  form  eliminated  and  with  two  equally 
smooth  and  polished  surfaces,  we  may  in  one  case,  have  marble,  and 
in  the  other,  granite.  The  relatively  greater  general  translucence  of 
the  marble  is  evident  and  is  recognized  by  the  eye,  and  this  does  not 
at  all  mean  that  the  object  must  be  held  between  the  eye  and  the  source 
of  the  light.  The  eye  is  trained  in  making  analysis  and  identifications 
of  this  kind.  The  surface  has  its  form,  variable,  characteristically 
modified  or  very  exact,  and  this  we  recognize.  Aside  from  that,  we 
see  below  the  immediate  surface  and  through  the  different  bodies 
which  may  be  of  every  degree  of  translucence  or  opacity.  The  object 
may  be  as  opaque  as  the  commercial  pigments,  themselves,  which  are 
selected  in  part  for  their  opacity,  but  this  is  very  rarely  the  case  in 
plant  and  animal  Hfe.  From  this  point  of  extreme  opacity,  there  will 
be  a  gradual  reduction  in  pigmentation  until  a  point  nearly  as  clear 
and  as  translucent  as  glass  is  found.  As  an  example,  in  a  snake  we 
have  a  nearly  colorless  transparent  scale  on  the  abdomen.  In  a  layer 
below  this  is  the  pigmentation  which  approaches  the  general  tone  of 
ivory.  In  making  a  reproduction  of  this,  it  is  necessary  to  reproduce 
all  the  parts  in  their  various  degrees  of  translucence  as  well  as  in 
correct  tint.  Also,  they  must  be  located  in  their  proper  order,  first 
the  nearly  transparent  surface  scale  and  then  below  this  the  successive 
colored  and  partly  translucent  areas.  Artificial  ivory  was  never  suc- 
cessfully reproduced  until  these  conditions  were  exactl}^  met.  Although 
ivory  and  its  natural  pigmentation  are  chemically  unrelated  to  the 
mediums  of  the  reproduction,  celluloid  and  zinc  white,  it  is  impossible 


14     Field  Museum  of  Natural  History — Technique,  No.  2. 

by  sight  alone  to  distinguish  between  the  real  and  the  artficial.  This 
is  due  to  correctness  of  details  in  regard  to  translucence  and  arrange- 
ment. The  vertebrate  eye  furnishes  an  exaggerated  example  of  such 
arrangements,  as  do  also  the  fins  and  scales  of  fish.  We  are  not 
deceived  by  these  outstanding  examples  as  we  are  with  the  more  subtle 
and  less  pronounced  problems  represented  in  the  great  majority  of 
subjects.  A  human  hand  furnishes  an  interesting  study  in  this  con- 
nection. The  veins  are  overlaid  by  a  rather  thick  dermal  coat  of  dif- 
ferent coloration.  The  nails  present  an  interesting  problem  of  a 
translucent  surface  with  the  coloration  in  the  underlying  parts. 

Another  type  of  coloration,  wholly  dependent  on  structural  forms, 
is  found  very  generally  in  fishes  and,  occasionally,  in  amphibians  and 
reptiles.  This  produces  the  iridescent  so-called  metallic  colors  which 
exist  in  combination  with  pigment  colors.  Often  their  source  is  deep- 
seated  but  in  other  cases  they  originate  on  or  are  reflected  from  the 
surface  of  the  scales  or  skin.  These  conditions  are  not  successfully 
reproduced.  Artificial  pearls  are  now  made  from  the  silvery  substance 
found  on  the  scales  of  small  fish.  An  industry  developed  in  the 
Mediterranean  regions  supplies  this  material.  This  substance  can  be 
dyed  or  colored  to  approximate  some  of  the  conditions  in  the  real 
pearl.  The  eflfects  seen  in  mother  of  pearl  are  due  to  minute  convolu- 
tions in  the  shell  layers.  The  combined  effect  of  the  numerous  trans- 
lucent shell  layers  is  barely  perceptible  when  a  cast  is  made  of  the 
surface  layer  only. .  With  but  few  exceptions,  the  coloration  due  to 
structural  forms  has  the  general  appearance  of  the  opal.  Opals  are 
not  now  artificially  reproduced,  so  at  the  present  time,  we  are  limited 
to  the  use  of  commercial  pigments,  dyes,  fish  scale  pearl  and  the  vari- 
ously colored  bronzes  as  coloring  agents  in  attempts  to  secure  the 
effect  of  this  type  of  coloration. 

Use  of  pigments  in  a  translucent  medium. — Excepting  the  examples 
of  structural  coloration  above  mentioned,  it  has  been  found  that  the 
conditions  of  coloration  can  be  reproduced  by  utilizing  ordinary  com- 
mercial pigments  added  in  carefully  guaged  amounts  to  a  translucent 
material.  In  practice,  the  transparent  material  is  reduced  to  a 
liquid  state  and  then  incorporated  with  the  appropriate  coloring  mate- 
rials. The  solvents  on  evaporation  leave  colored  translucent  masses 
that  can  be  made  to  resemble  any  particular  part  of  the  model.  In 
order  to  give  these  colored  masses  or  colored  layers  their  proper  location 
within  the  body  and  still  preserve  the  surface  detail  as  obtained  by 
molding,  the  colors  are  applied  to  the  interior  surface  of  the  mold  of 


FIELD    MUSEUM    OF   NATURAL   HISTORY. 


TECHNIQUE.    NO  2,    PL.    V. 


Fig.  1.    REPRODUCTION  OF  Green  Tree  Frog. 


Fig.    2.      MUHLENBERG'S  TURTLE. 
Reproduced  soft  parts  combineil  with  original  shell. 


ni.  2  4  1925 


Celluloid  in  Taxidermy — Walters.  15 

the  object,  first  the  surface  colors  and  following  these  the  underlying 
colors  or  markings  in  succession.  Each  section  can  be  given  its  proper 
relative  position  with  respect  to  the  surface  and  its  individual  degree 
of  translucence. 

The  thought  will  occur  that  this  is  not  so  much  a  process  of  coloring 
as  of  making  a  model.  This  is  exactly  the  case.  The  ideal  sought  is 
that  of  making  an  exact  duplicate  of  the  specimen  as  it  appears  in  life. 
Whatever  process  is  necessary  to  approach  this  ideal  must  be  adopted. 
The  colored  materials  are  to  be  washed  on,  put  on  with  a  knife,  needle, 
brush  or  by  any  method  that  serves  the  purpose  and  does  not  leave 
evidence  of  man's  handiwork.  Brush  marks  and  similar  effects  cannot 
by  any  process  of  reasoning  be  justified  here.  Reason  is  too  often 
clouded  by  custom  and  accepted  methods  of  an  established  art  tend  to 
be  used  regardless  of  real  applicability. 

Working  Mediums. 

Qualities  required  in  translucent  materials. — The  material  used  as 
a  translucent  basis  for  the  colors  should  be  in  the  original  state  as 
nearly  transparent  and  free  from  color  as  possible.  A  material  having 
an  initial  translucence  that  is  almost  perfect  is  necessary  in  obtaining 
the  brightest  tints.  The  working  out  of  complicated  patterns  and  the 
coloring  of  the  material,  itself,  call  for  its  reduction  to  a  liquid  state. 
It  must  permit  thickening  and  thinning,  and  applying  with  much  the 
same  facility  that  paints  and  varnishes  are  applied.  There  should  be, 
after  application,  a  reasonable  and  controllable  rapidity  in  drying  and 
solidifying.  The  materials,  themselves,  must  be  able  to  withstand  with- 
out change  the  conditions  to  which  the  finished  product  will  be  sub- 
jected. These  include  the  effects  of  dampness,  heat,  cold,  dust,  cleaning 
and  handling,  and  the  accidents  to  which  a  museum  specimen  is  subject 
in  the  course  of  time. 

Many  materials  which  are  useful  in  some  instances  cannot  be  used 
in  others.  All  have  their  disadvantages.  Any  material,  to  be  successful, 
will  require  much  study  and  experimentation,  and  to  say  that  a  par- 
ticular one  is  not  usable  may  only  mean  that  the  difficulties  have  not 
been  sufficiently  studied.  Casein  and  gelatine  have  qualities  that  make 
them  applicable  in  this  work.  The  varnish  gums  and  drying  oils,  and 
especially  linseed  oil,  are  valuable  and  useful.  Cellulose  acetate  and 
the  cellulose  nitrate  products,  pyroxylin  and  celluloid  have  been  most 
generally  used.  The  term  "pyroxylin"  applies  to  the  cellulose  nitrates 
that  are  soluble  in  amyl  acetate  and  other  commercial  solvents.  They 
have  a  nitrogen  content  varying  from  10.5  per  cent  to  12.2  per  cent 


i6     Field  Museum  of  Natural  History — Technique,  No.  2. 

and  are  used  in  lacquering  and  waterproofing  solutions,  in  the  manu- 
facture of  artificial  silk  and  leather,  and  in  many  other  processes  in 
which  the  handling  is  through  the  use  of  solvents.  Cellulose  nitrate, 
alone,  is  not  moldable,  but  when  it  is  mixed  with  camphor  the  resulting 
product,  with  the  aid  of  heat  and  pressure,  can  be  molded.  The  term 
"Celluloid"  was  the  first  trade  name  applied  to  this  product  and  is 
still  the  most  widely  known.  It  is  generally  established  as  applying 
to  all  the  moldable  cellulose  nitrates,  and  is  Used  here  in  this  sense. 
Other  well  known  trade  names  of  moldable  cellulose  nitrate  products 
are  "Pyralin,"  "Zylonite,"  "Xylonite,"  "Fiberloid,"  "Viscoloid,"  and 
"Cellonite."*  In  the  manufacture  of  pyroxylin,  primary  considerations 
are  uniformity  of  solubility  and  viscosity.  Celluloid  is  soluble  in  the 
usual  pyroxylin  solvents,  but  as  it  is  designed  for  molding  and  not  for 
use  as  a  lacquer,  there  is  much  variation  in  the  degree  of  solubility  and 
viscosity.  When  used  as  a  lacquer,  the  ingredient,  camphor,  while 
normally  of  no  value,  has  no  detrimental  effect. 

Cellulose  nitrates. — The  cellulose  nitrates,  in  their  original  state, 
are  transparent.  They  can  be  dissolved  in  a  rather  large  range  of 
solvents  for  many  and  varied  classes  of  work.  The  solvents  employed 
are  not  dangerous  to  health  if  common  precautions  are  taken  for  re- 
moval of  the  fumes  with  hoods  and  fans.  The  solutions  are  of  very 
high  viscosity,  said  to  be  seven  times  that  of  an  alcohol- shellac  solution, 
and  this  presents  much  difficulty  and  inconvenience  when  it  is  desired 
to  deposit  heavy  layers.  It  is  not  possible  to  reduce  this  viscosity 
greatly  although  there  are  means  by  which  it  can  be  lessened.  The 
flexibility  and  degree  of  hardness  of  pyroxylin  are  satisfactory.  Speci- 
mens made  of  this  material  will  withstand  accidental  blows  and  drop- 
ping on  the  floor  without  being  damaged.  It  is  water-proof  and  the 
specimen  can  be  washed  at  any  time  with  soap  and  water  and,  if 
necessary,  scrubbed  with  a  stiff  brush.  The  coloring,  being  beneath 
the  surface,  is  unaffected  by  any  kind  of  abuse  that  will  not  actually 
destroy  pyroxylin.  It  is  unaffected  by  ordinary  changes  of  tempera- 
ture. If  heated  to  336°  F,  it  decomposes,  but  as  a  general  rule  does 
not  inflame.  If  a  sample  is  brought  into  contact  with  a  flame,  it  will 
ignite  and  the  flame  will  travel  through  the  mass,  but  it  can  generally 
be  extinguished  by  a  sharp  breath  of  air.    It  is  interesting  to  note  that 


*For  information  on  the  general  subject,  without  reference  to  the  particular 
problems  of  the  taxidermist,  two  important  works  by  C.  E.  Worden  are  avail- 
able.    These  are: 

Nitrocellulose  Industry.    2  Vols.     New  York,  191 1. 

Technology  of  Cellulose  Esters.    D.  Van  Nostrand  Co.,  New  York,  1916, 


FIELD   MUSEUM   OF  NATURAL  HISTORY. 


TECHNIQUE.    NO.    2.    PL.    VI. 


Face  of  Black  Howling  Monkey. 
Reproduced  soft  parts  combined  with  original  hair.     (.Muzzle  slightly  foreshortened) 


J'Ji.  2  4  1925 


Celluloid  in  Taxidermy — Walters.  17 

holes  can  be  bored  through  a  mass  or  sheet  of  celluloid  with  a  red  hot 
iron  without  the  ignition  of  the  mass.  Opticians  often  wave  celluloid 
spectacle  frames  back  and  forth  above  a  flame  in  order  to  heat  suffi- 
ciently for  bending. 

Cellulose  nitrate  and  its  products,  in  the  original  state  and  without 
additions,  are  subject  to  deterioration.  This  is  said  to  be  due  to  faulty 
methods  of  manufacture  and  to  the  fact  that  the  nitric  acid,  while 
originally  combining  with  the  cellulose,  tends  in  time  to  free  itself  from 
combination.  In  the  free  state,  it  affects  the  cellulose,  making  it  more 
brittle  and  giving  the  mass  a  characteristic  brownish  tinge.  This  action 
is  hastened  by  exposure  to  heat  and  light.  Such  deterioration  does  not 
always  take  place,  at  least  not  at  the  same  rate,  for  some  samples  do 
not  show  perceptible  change  after  several  years  of  exposure.  The 
brittleness  is  not  of  serious  consequence  as  it  is  only  evident  on  flexing, 
and  in  this  work  the  surface  coatings  are  joined  to  a  solid  structure, 
but  the  change  of  color  is  very  important  as  all  the  brighter  colors 
would  be  affected.  Any  neutralizer  of  the  acid  as  it  develops,  will 
retard  or  entirely  offset  this  detrimental  action.  The  range  of  neutral- 
izers  that  can  be  incorporated  in  a  water  white  celluloid,  and  still  not 
affect  its  clearness,  is  limited.  With  pigmented  celluloid,  however,  a 
large  range  of  effective  neutralizers  is  available,  most  pigments  as  well 
as  white  lead  and  zinc  white  rendering  the  product  stable.  I  have 
organ  keys  containing  zinc  white  as  the  pigment  which  show  no  ap- 
parent deterioration  after  forty  years.  In  view  of  the  uncertainty  as 
to  the  stability  of  different  samples  of  cellulose  nitrate,  it  is  desirable 
to  use  celluloid,  pyralin  or  similar  material  that  has  withstood  the 
effects  of  time  and  exposure  incident  to  service  for  at  least  several 
years,  and  has  still  retained  its  original  clear  color  and  flexibility.  To 
this,  when  reduced  to  a  lacquer,  neutralizers  should  be  added  as  a 
further  precaution,  and  in  coloring,  so  far  as  possible,  acid  neutralizing 
pigments  should  be  incorporated.  Although  this  practice  may  not  be 
entirely  sound,  it  seems  to  justify  the  use  of  celluloid  instead  of  py- 
roxylin, the  cellulose  nitrate  which  is  designed  for  and  is  best  adapted 
for  lacquer  work. 

Cellulose  acetate. — When  cellulose  is  treated  with  a  mixture  of 
acetic  anhydride  and  acetic  acid,  products  are  obtained  having  the  ap- 
pearance and  general  properties  of  the  cellulose  nitrates  but  possessing 
also  some  distinct  advantages.  These  are  known  as  the  cellulose  acet- 
ates. Cellulose  acetate  is  not  moldable  but  becomes  so  with  the  addition 
of  camphor.     "Cellit"  is  a  trade  name  given  to  a  cellulose  acetate  con- 


i8     Field  Museum  of  Natural  History — Technique,  No.  2. 

taining  camphor  and  stands  in  the  same  relation  to  cellulose  acetate 
that  celluloid  does  to  the  cellulose  nitrates. 

Cellulose  acetate  has  the  hardness,  the  flexibility,  and  the  initial 
transparence  of  the  cellulose  nitrates.  In  motion  picture  films,  in 
which  it  has  the  greatest  field  of  use,  it  is  much  less  inflaminable  than 
the  nitrate.  Although  inflammability  is  frequently  m.entioned  in  con- 
nection with  museum  preparations,  it  is  really  of  little  consequence. 
The  finished  specimens  will  never  be  subjected  to  such  conditions  as 
prevail  in  the  use  of  films,  and  a  case  of  spontaneous  ignition  in  an 
isolated  body  of  cellulose  nitrate,  if  it  does  occur,  must  be  very  rare. 
We  are  surrounded  by  innumerable  cellulose  nitrate  products  and  it  is 
probable  that  no  one  reading  this  has  ever  personally  experienced  a 
case  of  spontaneous  combustion  in  such  a  body.  Cellulose  acetate,  when 
subjected  to  tests,  shows  a  stability  much  beyond  that  of  the  nitrate. 
It  also  has  an  advantage  over  the  nitrate  in  the  fact  that  any  possible 
release  of  the  acetic  acid  used  in  its  manufacture  can  do  no  harm,  as 
acetic  acid  does  not,  in  small  quantities,  have  a  harmful  eflFect  on  cel- 
lulose. Solutions  of  cellulose  acetate  have  an  equally  high  viscosity 
when  compared  with  the  nitrate.  Many  solvents  are  common  to  the 
two,  while  each  has  a  series  of  solvents  in  which  the  other  is  insoluble. 

Future  Problems. 

Technical  study. — An  extended  technical  study  is  necessary  for  the 
successful  handling  of  cellulose  acetate  and  cellulose  nitrate  and  their 
products.  The  actions  and  properties  of  the  solvents  and  non-solvents 
utilized  must  be  tested  by  many  experiments.  Progress  is  not  possible 
without  study  and  familiarity  with  the  materials  sufficient  to  enable  the 
compounding  of  formulae  to  fit  the  many  variable  needs  as  they  arise. 
These  problems  must  be  experienced  to  be  understood.  For  reference, 
a  record  of  all  formulae  and  experiments,  whether  successful  or  not, 
should  be  kept  on  filing  cards.  There  are  many  interesting  problems 
of  technique  which,  at  the  present  time,  are  not  completely  solved. 
Rapid  progress  is  being  made  and  it  is  hoped  to  reach  definite  conclu- 
sions, soon,  in  regard  to  the  most  important  matters.  Full  discussion 
of  these  would  be  premature  and  is  beyond  the  scope  of  this  paper. 

Scope  and  possibilities. — Although  especially  adapted  and  first  ap- 
plied to  reptiles  and  amphibians,  the  foregoing  discussion  of  principles 
and  methods  applies  to  practically  every  branch  of  work  with  which 
a  museum  preparator  has  to  contend.  Plants  with  complicated  colora- 
tion often  present  details  of  surface  form  that  it  is  desirable  to  pre- 


Celluloid  in  Taxidermy — Walters.  19 

serve  exactly.  The  feet  and  bills  and  exposed  skin  surfaces  on  the 
heads  and  bodies  of  birds  are  important  subjects.  Young  birds  are 
outstanding  examples.  Many  of  them  are  entirely  naked,  and  the  tis- 
sues are  often  so  translucent  that  the  viscera  and  other  abdominal 
organs  and  many  of  the  bones  are  distinguishable.  Thinly  haired 
mammals  or  mammals  with  exposed  skin  surfaces  are  subjects  in  which 
the  skin  coloration  and  fine  details  of  form  are  of  vital  importance  in 
connection  with  a  life-like  appearance.  Most  of  the  young  of  mammals 
are  hairless.  Many  others  are  so  thinly  haired  that  the  glow  of  the 
skin  surface,  especially  with  the  lighter  fleshy  tints,  decidedly  affects 
the  general  color  appearance.  To  extend  these  methods  to  mammal 
work,  the  variation  from  the  regular  procedure  requires  a  method 
which  provides  for  the  correct  transference  of  the  hair.  This  first 
calls  for  the  construction  of  an  armature  and  a  clay  figure  in  the  ordi- 
nary way.  The  skin  in  a  freshened,  soft  and  plump  condition  is  ad- 
justed on  this  form.  The  molding  material,  typically  plaster,  is  applied  in 
such  manner  as  to  entirely  surround  the  individual  hairs  and  take  an 
exact  impression  of  the  skin  surface  between.  When  the  mold  is 
completed  and  re-enforced,  it  is  separated  along  lines  previously  estab- 
lished, and  the  interior  clay  structure  removed,  the  skin  remaining 
attached  to  the  mold  by  the  embedded  hair.  Through  dehairing  treat- 
ments, such  as  are  in  use  in  tanning  operations,  the  tissues  surrounding 
the  hair  roots  are  acted  upon  and  the  skin  detached  and  removed  from 
the  mold.  The  mold  then  presents  an  accurate  negative  of  the  skin 
surface  with  the  root  of  each  hair  protruding  and  exposed.  The  colors 
are  prepared  and  applied  in  the  usual  manner,  the  liquid  cellulose 
acetate  or  nitrate  surrounding  each  hair  root.  On  the  evaporation  of 
the  solvent,  the  hair  is  left  enclosed  and  embedded  in  the  solidified 
material.  As  a  means  of  support,  this  artificial  skin  is  continued  into 
alternate  layers  of  cloth  and  wire  cloth,  the  resulting  structure  being 
similar  to  that  used  in  ordinary  mammal  work.  The  removal  of  the 
mold  leaves  the  specimen  complete  with  the  natural  hair  set  in  an 
artificial  skin  which  has  correct  color  and  translucence.  In  this  mam- 
mal work,  molds  have  been  made  of  plaster  compositions,  of  waxes 
and  of  other  materials  and,  therefore,  different  methods  of  removing 
them  have  been  employed. 

Future  Taxidermy. — The  idea  is  widely  accepted  that  taxidermy  is 
necessarily  an  art  of  low  standing.  It  is  full  of  great  technical  diffi- 
culties and  these  are  sufficient  to  account  for  the  grade  of  work  pro- 
duced from  which  opinion  is  formed.     As  these  difficulties  are  over- 


20    Field  Museum  of  Natural  History — Technique,  No.        2. 

come,  a  gradual  recognition  of  its  possibilities  and  an  increasing  interest 
in  it  may  take  place. 

Sculpture  is  devoted  to  expression  through  form.  Stone  and  metals, 
into  which  its  work  is  finally  translated,  preclude  the  possibility  of 
complete  realism.  Such  realism  is  dependent  not  only  on  color  and 
general  form  but  on  the  most  minute  detail  of  the  surface  structure. 
This  can  only  be  obtained  by  direct  molding  of  actual  surfaces ;  it 
cannot  be  modelled  in  clay  or  cut  in  marble  and  is,  therefore,  outside 
the  possibilities  of  sculpture. 

Realism,  therefore,  is  the  province  of  taxidermy.  It  has  a  distinct 
field  of  its  own,  well  worthy  of  the  best  effort.  In  this  field,  the  pos- 
sibihties  by  no  means  have  been  exhausted  and  it  is  to  be  hoped  that 
the  future  may  see  much  further  progress. 


EXPLANATION  OF  PLATE  VIL 

Fig.  I.     Waste  mold  of  a  crocodile,  made  in  four  pieces,  two  of  which  are  joined. 

Fig.  2.  The  mold  after  partial  application  of  pigmented  celluloid.  The  coloring 
is  continued  and  followed  by  reenforcing  materials  to  give  strength 
to  the  model.  The  preserved  skin  shown  in  the  foreground  is  used 
as  a  guide  for  color  pattern  but  the  tints  are  based  on  detailed  field 
notes. 

Fig.  3.  The  completed  model  of  the  walking  crocodile,  shown  in  Plate  IH, 
emerging  from  its  plaster  case.  The  plaster,  softened  by  water,  is 
chipped  away  with  hammer  and  chisel. 


FIELD   MUSEUM   OF   NATURAL  HISTORY. 


TECHNIQUE,    NO.    2.    PL.    VII. 


i1;l  imm  w^  m 


/  1925 


U^'IYCP"ITY  OF  il 


UNIVERSITY  OF  ILLINOIS-URBANA 


3  0112  074281350 


